This standard specifies the dry and wet magnetic particle (including fluorescent and non-fluorescent) flaw detection methods and quality grade assessment of pump product parts. This standard is suitable for inspecting surface and near-surface defects of pump product parts made of ferromagnetic materials. JB/T 6912-1993 Non-destructive testing of pump product parts and magnetic particle testing JB/T6912-1993 Standard download and decompression password: www.bzxz.net

Machinery Industry Standards of the People's Republic of China
Non-destructive testing of pump product parts
Magnetic particle testing
Theme content and scope of application
JB/T 6912--93
This standard specifies the dry and wet magnetic particle (including fluorescent and non-fluorescent) flaw detection methods and quality grade assessment of pump product parts. This standard is suitable for inspecting surface and near-surface defects of pump product parts (hereinafter referred to as workpieces) made of ferromagnetic materials. 2 Reference standards
GB3721 Magnetic particle flaw detector
GB5097
Indirect assessment method of black light source
GB/T12604 Non-destructive testing terminology
ZBH24006 Magnetic particle for steel materials Flaw detection method 3 Terminology
The terms and definitions in this standard are in accordance with GB/T12604. 4. Flaw detection personnel
4.1. Flaw detection personnel should pass the assessment of relevant departments before they can take up their duties. The person who issues the flaw detection report should hold a qualification certificate for magnetic particle flaw detection of at least Level II.
4.2 Those who are color blind and whose corrected visual acuity at close range is below 1.0 are not allowed to participate in the magnetic particle inspection assessment. 4.3 Flaw detection personnel should be equipped with protective equipment and operate in accordance with relevant regulations. 5 Flaw detection timing
5.1 Flaw detection should be carried out after the final heat treatment and finishing of the workpiece (unless otherwise required by the user). 6 Flaw detection equipment
6.1 Magnetic particle detection equipment shall comply with the requirements of GB3721. 6.2 When using the residual magnetism method for detection, the AC flaw detector should be equipped with a power-off phase controller. 6.3 When using fluorescence method for detection, the ultraviolet intensity of the ultraviolet lamp used on the surface of the workpiece should not be less than 1000uW/cm2, and the wavelength of ultraviolet light should be in the range of 0.32-~0.40μm. 6.4 The demagnetization device should be able to ensure that the surface magnetic field intensity of the workpiece after demagnetization is less than 160A/m. 6.5 In order to ensure the reliability of magnetic particle inspection equipment, the following calibrations should be carried out: a. Under normal circumstances, the ammeter should be calibrated at least once a year; b. When the electromagnetic yoke pole spacing is 50 to 200mm, the AC electromagnetic yoke should have a lifting force of at least 44N, and the DC electromagnetic yoke should have a lifting force of at least 177N;
c.
The illumination of the ultraviolet lamp should be According to the requirements of GB5097, measurement should be carried out once a year. The Ministry of Machinery Industry of the People's Republic of China approved 426
1994-07-01 implementation
JB/T 6912--93
6.6 on 1993-07-13 to ensure the smooth progress of magnetic particle testing work , the following auxiliary equipment should be provided: a. Magnetic field indicator (octagonal test block), type A test piece, type C test piece: magnetic suspension concentration measuring tube:
b.
c.
2~~10x magnifying glass.
6.7 When using fluorescent magnetic particle testing, the following auxiliary equipment should also be provided: magnetic field strength meter;
a.
b. Light meter;
c. UV lamp;
d． UV lamp intensity meter.
7Magnetic powder
7.1 The particle size of magnetic powder should be uniform. The average particle size of the magnetic powder used in the method is 2~~10um, and the maximum particle size should not be larger than 45μm: the average particle size of the magnetic powder used in the dry method should not be larger than 90um, and the maximum particle size should not be larger than 180um. 7.2 The color of the magnetic powder should be compared with the surface of the workpiece being inspected. Has a higher contrast ratio. 7.3 Wet powder method should use kerosene or water as the dispersion medium. If water is used as the medium, appropriate rust inhibitors and surfactants should be added. The viscosity of the magnetic suspension is 500~2000Pa·s (at 25℃). 7.4 The concentration of the magnetic suspension should be determined according to the type and particle size of the magnetic powder as well as the application method and time. The concentration of the newly prepared non-fluorescent magnetic powder is 10~20 g/L, and the concentration of fluorescent magnetic powder is 1~3 g/L. 7.5 When the magnetic suspension is recycled, the concentration of the magnetic suspension should be measured regularly. In every 100mL of magnetic suspension, the precipitation volume of non-fluorescent magnetic powder is 1.2~2.4mL, and the precipitation volume of fluorescent magnetic powder is 0.1~~0.5ml-. Before measurement, the magnetic suspension should be fully stirred through the circulation system for no less than 30 minutes.
8 Workpiece surface preparation
8.1 The surface roughness Ra value of the inspected workpiece is 25μm. 8.2 There should be no grease or other substances that can adhere magnetic particles to the surface of the workpiece being inspected. 8.3 If the oil holes and other pores of the inspected workpiece are difficult to remove magnetic particles after flaw detection, they should be blocked with harmless substances before flaw detection. 8.4 In order to prevent the arc from burning the surface of the workpiece and improve the conductive performance, the contact area between the workpiece and the electrode should be cleaned, and if necessary, a contact pad should be installed on the electrode.
9 Magnetization method
9.1 Longitudinal magnetization
When detecting defects perpendicular to the axis of the workpiece or at an angle greater than 45°, longitudinal magnetization should be used. Longitudinal magnetization can be obtained by the following method:
Coil method (Figure 1):
a.
Defect
Line warp
Current||tt| |Figure 1
427
b.
Yoke method (Figure 2).
9.2 Circumferential Magnetization
Core
Workpiece
Defects
JB/T 6912—-93
Figure 2||tt ||When detecting defects that are parallel to the axis of the workpiece or at an angle less than 45°, circumferential magnetization should be used. Circumferential magnetization can be obtained by the following methods:
a. Axial energization method (Figure 3):
Electrode
Current
Central conductor method (Figure 4)
b.
Current||tt| |c.
Contact method (Figure 5).
428
Work piece
Defects
Picture 3
Defects
Picture 4
Electrode trigger||tt| |Electricity
Defects
Figure 5
Work piece
Center conductor
Work piece
9.3 Power supply method
JB/T 6912-93
The workpiece magnetization and energization methods are divided into continuous method and magnetic method. 9.3.1 When using the continuous method, the application of magnetic powder or magnetic suspension should be completed within the power-on time. The power-on time is 1~~3s. To ensure the magnetization effect, magnetization should be repeated at least twice, and the magnetization can be stopped only after stopping the application of magnetic suspension for at least 1 second. 9.3.2 When using the residual magnetization method, the magnetic powder should be applied after the end of energization, and the energization time is 0.25 to 1%. When using impulse current, the energization time should be above 0.01s and the magnetization should be repeated at least three times. 9.3.3 When using the AC breeding method, a power-off phase controller should be equipped to ensure the magnetization effect of the workpiece. 9.4 Magnetized area
Each inspected area of ??the inspected workpiece should be inspected at least twice independently, and the directions of the magnetic lines of force in the two inspections should be approximately perpendicular to each other. When conditions permit, rotating magnetic field and AC and DC composite magnetization methods can be used. 10 Magnetization specifications
10.1 Sensitivity test piece
10.1.1A type sensitivity test piece is only suitable for the continuous method and is used for the effective magnetic field strength and direction on the surface of the inspected workpiece, the effective detection area and the flaw detection method correct measurement. The magnetizing current should be able to show clear magnetic marks on the test piece. 10.1.2A type sensitivity test piece has three levels of sensitivity: high, medium and low. Its geometric dimensions are shown in Figure 6, and its model and groove depth are shown in Table 1. 20
Thickness 0.1
Depth 0.012|| tt||Figure 6
Table 1
Model
A-15/100
A-30/100
A-60/100|| tt||relative groove depth
%
sensitivity
high
medium
low
Note: relative groove depth expression of test piece , the numerator is the depth of the artificial groove, and the denominator is the thickness of the test piece. Material
um
Ultra high purity low carbon pure iron (C<
0.03%, H≤80 A/m, after annealing
fire treatment)||tt ||10.1.3 When testing a small area and it is inconvenient to use the type A sensitivity test piece, the type C sensitivity test piece can be used. The geometric dimensions of the C-type tenderness test piece are shown in Figure 7, and the model and groove depth are shown in Table 2. 429
Type
No.
C
Thickness||tt ||50
JB/T 6912--93
Separating line
Figure 7
Table 2
Manual defects
Manual defects Depth
8±1
Material
am
Super commercial pure low carbon pure iron (C<0.03%,
H<80A/m, After annealing)
10.1.4. The magnetic field indicator (octagonal test block) is a rough detection tool used to indicate the direction of the magnetic field on the surface of the workpiece being inspected, the effective detection area and whether the magnetization method is correct, but it cannot be used as a quantitative indication of the magnetic field strength and its distribution. Its geometric dimensions are shown in Figure 8. Non-magnetic handle
Artificial defects
8 pieces of low carbon steel, brazed together into one
Copper sheet with a thickness of 0.25±0.025
Picture 8||tt ||10.1.5 How to use sensitivity test pieces
When using type A or type C sensitivity test pieces, the side without artificial defects of the test piece should face outward. In order to ensure good contact between the test piece and the surface to be inspected, transparent tape can be used to flatly paste it on the surface to be inspected. Note that the tape should not cover artificial defects on the test piece. When testing, the continuous magnetization method should be used.
b． When using a magnetic field indicator, you should magnetize the workpiece using the continuous method, place it flat on the surface to be inspected, and apply magnetic suspension to the surface, so that "×" shaped magnetic marks appear to identify the workpiece. Magnetization is appropriate or not. 10.2 Axial energization method
When axially energizing magnetization, the magnetizing current is calculated according to formula (1), formula (2), and formula (3) respectively: DC (rectifier) ??continuous method
I (12 -- 20)D
Direct current (rectifier) ??residual magnetization method
430
(1)
Alternating current continuous method
Where: I-
Current value A:
Maximum size on the cross-section of the workpiece, mm.
D
JB/T 6912--93
I = (25 -- 45)D -
I (6 ~ 10)D
10.3 Contact method
10.3.1 When using the contact method to locally magnetize large workpieces, the magnetizing current value is shown in Table 3. Material thickness T
mm
20
20
Table 3
Current value!
A
3~4 times the contact distance
4~~5 times the contact distance
f
(3)||tt| |10.3.2 When using the contact method, the electrode spacing should be controlled between 75 and 200mm, and the contact between the electrodes and the workpiece should be maintained well to avoid burning the workpiece.
10.4 Center conductor method
10.4.1 The center conductor method should be used as much as possible for the magnetization of the inner surface of hollow or porous parts. The material of the center conductor is preferably copper, and the diameter of the center conductor should not be less than 10% of the diameter of the inner hole of the workpiece. The center conductor can be placed centrally or off-center. When placed eccentrically, the distance between the center conductor and the inner surface of the workpiece is 10 to 15 mm. The effective detection area each time is approximately 4 times the diameter of the central conductor (see Figure 9) and should have a certain overlapping area, and the length of the overlapping area should not be less than 0.4d. Figure 9
10.4.2 The magnetizing current value when the diameter of the central conductor is 50mm is shown in Table 4. Table 4
Wall thickness T
mm
6
>6-9
>9～12
>12 ~15| |tt||Current value
A
1000
1250
1500
1750
431
JB/T 6912-93
When the wall thickness is greater than 15mm, the current increases by 250A for every 3mm increase in thickness. When the diameter of the central conductor is increased or decreased by 12.5mm from the specified value, the current value will be increased or decreased by 250A accordingly. 10.5 Yoke method
10.5.1 When using a yoke to magnetize the workpiece, the magnetizing current should be determined based on the sensitivity test piece or the lifting test. 10.5.2 The magnetic pole spacing of the yoke is 50~200mm, and the effective detection area is within the range of 50mm on both sides of the line connecting the two magnetic poles. The magnetized areas should overlap by 15mm each time.
10.6 Coil method
10.6.1 When using a low filling factor coil to longitudinally magnetize the workpiece, the diameter of the workpiece (or the transverse dimension equivalent to the diameter) should not be larger than the inner diameter of the fixed annular coil 10%. The workpiece can be placed eccentrically or centrally in the coil. When placed eccentrically, the magnetizing current of the line diagram is calculated according to formula (4): 45000bzxz.net
I
N(/D)
where: "——Current value, A;| |tt||N.—-Number of coil turns
I—Workpiece length, mm;
D-
Workpiece diameter or maximum size on cross section, mm The magnetizing current is calculated according to formula (5): b.
1.720R
1 = N[6(L/D)=5]
where: R-||tt ||Coil radius, mm
+--
.(4)
.*.*.(5)
10.6.2 For fixed wires that are not suitable For large workpieces, cable-wound coils can be used for detection. When magnetizing, calculate the magnetizing current according to equation (6):
35000
1 = N(/D)+2)||tt. ||(6)
10.6.3 The above formula is not applicable to workpieces with aspect ratio (L/D) less than 3. For workpieces with (L/D) less than 3, if the coil method is used, it can be used. Use the magnetic pole extension block to increase the effective value of the aspect ratio or use the actual measurement of the sensitivity test piece to determine the value of 1. For workpieces with (1./D) ≥ 10, (L/D) in the formula is 10. .4 The effective magnetization area of ??the line circle method is within the range of 0.5 times the diameter of the coil outside the coil end. 10.6.5 When the workpiece to be inspected is too long, it should be magnetized in sections, and there should be a certain overlap area. Should not be less than 10% of the segmented detection length.
11 Apply magnetic powder
After the workpiece is magnetized, one of the following methods can be used to apply magnetic powder 11.1 Dry powder method
In the dry powder method. Magnetic powder can be applied with a manual or electric duster and other suitable tools. The magnetic powder should be evenly sprinkled on the inspected surface of the workpiece, and the amount of magnetic powder should be appropriate so as not to cover up the defective magnetic traces and should not interfere with the magnetic defects when blowing off the excess magnetic powder. 11.2 Wet powder method
11.2.1 When using the wet powder method, it should be confirmed that the entire flaw detection surface can be well wetted by the magnetic suspension; 11.2.2 The application of the magnetic suspension can be done. Methods such as pouring and dipping should be used instead of brushing. No matter which method is used, the flow rate of the magnetic suspension on the flaw detection surface should not be too fast.
12 Demagnetization
12.1 Flaw detection completed Generally, it should be demagnetized.
12.2 If there are no special requirements for circumferentially magnetized parts, and parts that need to be heated after flaw detection, they may not be demagnetized. 432
JB/T 6912-
12.3 Demagnetization generally involves placing the workpiece into a magnetic field equal to or greater than the magnetized workpiece, and then continuously changing the direction of the magnetic field while gradually reducing the magnetic field intensity to zero
12.3.1 AC demagnetization method
The workpiece to be demagnetized is slowly withdrawn from the energized magnetizing coil until the workpiece is more than 1㎡ away from the coil, and then the current is cut off. Or, after the workpiece is placed in the energized magnetizing coil, the current value in the coil diagram is gradually reduced to zero. 12.3.2 DC demagnetization method
Place the workpiece to be demagnetized in the DC electromagnetic field, continuously change the direction of the current, and gradually reduce the current value to zero. 12.3.3 Demagnetization of large workpieces
Large workpieces can Use an AC electromagnetic yoke for local demagnetization or use wound cable coils for segmented demagnetization. 12.4 The demagnetization effect of the workpiece is generally measured with a residual magnetometer or magnetometer. 13 Evaluation of magnetic thinness
13.1 Except for the fact that the magnetic marks can be definitely determined to be caused by local uneven magnetism of the workpiece material or improper operation, other magnetic marks should be treated as defective magnetic marks.
13.2 Defect magnetic marks with a length-to-width ratio greater than 3 shall be treated as linear defects; defective magnetic marks with a length-to-width ratio less than or equal to 3 shall be treated as circular defects.
13.3 When the angle between the magnetic defect mark and the workpiece axis or busbar is greater than or equal to 30°, it will be treated as a transverse defect, and other defects will be treated as a longitudinal defect.
13.4 When defective magnetic traces are on the same line and the distance is less than or equal to 2mm, it shall be treated as one defect, and its length shall be the sum of the two defects plus the distance.
13.5 Non-crack longitudinal defect magnetic marks with a length less than 1mm and non-crack transverse defect magnetic marks with a length less than 0.5mm are not counted in the assessment.
13.6 If the magnetic defect mark is located at the junction of the important area and the non-important area of ??the workpiece, it will be counted as the important area. 13.7 According to the different stress conditions of each part of the workpiece, the surface of the workpiece can be divided into important areas (Area A) and non-important areas (Area B). 13.7.1. The division of important areas (area A) and non-important areas (area B) of the pump shaft, crankshaft, and connecting rod is shown in Figure 10, Figure 11, and Figure 12. Area B
Area A
a;—0.1d and a;≥25(i--1,2,3.-)Figure 10
433
B Area
JB/T 6912--93
Area B
a=0.1d and a≥25
Figure 11
Area||tt ||Area
No.+8
Figure 12
13.7.2 Welds, threaded areas, mating surfaces, sealing surfaces, transition fillets, and keyways in other parts and components (Oil hole) The 2d range is an important area (Area A), and the rest is a non-important area (Area B). 14 Re-inspection
When one of the following situations occurs, re-inspection shall be carried out in accordance with the relevant provisions in Chapters 8 to 13. 434
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